Piston metering pumps of the general type involved herein are old and well known. In such prior art pumps, the portion of the piston assembly cooperating with the motor driven eccentric is machined from bar stock in a manner which requires several different types of machinery, requires great skill, is time consuming, whereby the piston assembly is an expensive component of the pump.
The present invention recognizes these disadvantages of the prior art and teaches the novel structural interrelationship which minimizes the cost of manufacture of the piston assembly with less capital equipment and less skill being required.